JPH05323194A - Rear focus type zoom lens - Google Patents

Abstract

(57) [Abstract] [Purpose] There are four lens groups as a whole, and the zoom ratio is 8
To obtain a rear focus type zoom lens having high optical power and excellent optical performance over the entire zoom range and the entire object distance. [Structure] The first, second, third, and fourth groups of positive, negative, positive, and positive refractive powers are arranged in this order from the object side, and zooming is performed in the second group, and image plane variation accompanying zooming is performed. And focus in the fourth group,
The third group is composed of a positive 31st lens having an aspherical surface,
The fourth group is composed of a negative lens and a positive lens, and the focal lengths of the combined system and the entire system of the third group and the fourth group at the wide-angle end are f
When the shortest back focus at 3, 4, FW and infinity focus is Fb and the zoom ratio is Z

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rear focus type zoom lens, and more particularly to a large aperture ratio of about 8 to 10 and an F number of about 1.8, which is used for photographic cameras, video cameras, broadcast cameras and the like. The present invention relates to a rear focus type zoom lens having a high zoom ratio and a short overall lens length.

[0002]

2. Description of the Related Art Hitherto, various zoom lenses for photographic cameras, video cameras and the like have been proposed which employ a so-called rear focus type in which focusing is performed by moving a lens unit other than the first lens unit on the object side. ing.

Generally, in a rear focus type zoom lens, the effective diameter of the first lens group is smaller than that of a zoom lens in which the first lens group is moved to perform focusing, which facilitates downsizing of the entire lens system and close-up photography. Especially, it is easy to perform very close-up photography, and since the relatively small and lightweight lens group is moved, the driving force of the lens group is small, and quick focusing is possible.

As such a rear focus type zoom lens, for example, in Japanese Patent Laid-Open No. 63-44614, a first lens group having a positive refractive power, a second lens group having a negative refractive power for zooming, and a zoom lens are arranged in order from the object side. In a so-called 4-group zoom lens composed of four lens groups, a third lens group having a negative refractive power and a fourth lens group having a positive refractive power, for correcting the image plane variation due to doubling, the third lens group is moved. Focus is on. However, this zoom lens tends to increase the total length of the lens because it is necessary to secure a moving space for the third lens group.

In Japanese Patent Laid-Open No. 58-136012, the variable power portion is composed of three or more lens groups, and some of these lens groups are moved for focusing.

In JP-A-63-247316 and JP-A-62-24213, the first group having a positive refractive power, the second group having a negative refractive power, and the third group having a positive refractive power are sequentially arranged from the object side. group,
Then, it has four lens groups of the fourth lens group having a positive refractive power, moves the second lens group to perform zooming, and moves the fourth lens group to perform image plane variation and focus accompanying zooming. ..

In JP-A-58-160913, a first group having a positive refractive power, a second group having a negative refractive power, are arranged in this order from the object side.
The third lens unit has a positive refracting power and the fourth lens unit has a positive refracting power, and there are four lens units. The first lens unit and the second lens unit are moved to perform zooming, and the image plane changes due to zooming. Is performed by moving the fourth group. Then, one or more of these lens groups are moved to perform focusing.

[0008]

In recent years, miniaturization of solid-state image pickup devices (CCD) as image pickup means in video cameras has been advanced. For example, in place of the conventional solid-state image sensor of 2/3 inch or 1/2 inch, a small image sensor of 1/3 inch or 1/4 inch has been used.
Further, a smaller size is required for the zoom lens used accordingly.

Further, in the taking lens used in the video camera, the distance from the final lens surface to the image pickup surface is prevented so that dust and dirt adhering to the final lens surface is not projected on the image pickup element surface and adversely affects the image. That is, the back focus is relatively long.

However, for example, when the zoom lens configured for the 1/2 inch image pickup device is used for the 1/4 inch image pickup device and the size of the zoom lens is simply reduced proportionally, the back focus is also proportional to it. It becomes shorter (it becomes 1/2). Then, dust or the like adhering to the final lens surface appears on the surface of the image pickup device, and the image quality is degraded. Therefore, even if the image pickup device is downsized, it is necessary to use a zoom lens having a back focus longer than a certain length for a video camera.

In general, when a rear focus system is adopted in a zoom lens, the entire lens system is downsized and quick focusing becomes possible.

On the other hand, on the other hand, the fluctuation of aberration at the time of focusing becomes large, and it becomes very difficult to obtain high optical performance while miniaturizing the entire lens system over the entire object distance from an infinite object to a short-distance object. The problem arises. In particular, in a zoom lens having a large aperture ratio and a high zoom ratio, it becomes very difficult to obtain high optical performance over the entire zoom range and the entire object distance.

According to the present invention, while adopting the rear focus system, a large aperture ratio and a high zoom ratio are achieved, and at the same time, the entire lens system is downsized, and the zoom range is widened from the wide-angle end to the telephoto end. An object of the present invention is to provide a rear focus type zoom lens having good optical performance and a predetermined back focus over the entire object distance from an object at infinity to an object at a short distance.

[0014]

A rear focus type zoom lens according to the present invention comprises a first group having a positive refractive power, a second group having a negative refractive power, and a third group having a positive refractive power in order from the object side. , And a fourth lens unit of a fourth lens unit of positive refractive power,
The lens unit is moved to the image plane side to perform zooming from the wide-angle end to the telephoto end, and the image plane variation due to zooming is corrected by moving the fourth lens unit and moving the fourth lens unit to focus. And the third group consists of a positive thirty-first lens having an aspherical surface, the fourth group consists of a negative forty-first lens and a positive forty-second lens,
At least one lens surface of the forty-first lens and the forty-second lens is made of an aspherical surface, and the combined focal lengths of the third group and the fourth group at the wide-angle end are f3, 4 and the focal length of the entire system at the wide-angle end. Is Fw, Fb is the distance from the final lens surface to the image plane (back focus) that is the shortest in the entire zoom range while focusing on an object at infinity, and Z is the zoom ratio.

[0015]

[Equation 5] It is characterized by satisfying the following condition.

[0016]

1 is a schematic view of an embodiment showing the paraxial refractive power arrangement of a rear focus type zoom lens according to the present invention. 2 to 4 are lens cross-sectional views of Numerical Examples 1 to 7 described later.

In the figure, L1 is a first group having a positive refractive power, L2 is a second group having a negative refractive power, L3 is a third group having a positive refractive power, and L4.
Is the fourth group of positive refractive power. SP is an aperture stop,
It is arranged in front of the third unit L3. G is an optical member such as a face plate.

At the time of zooming from the wide-angle end to the telephoto end, the second lens unit is moved to the image plane side as indicated by the arrow, and the image plane variation due to zooming is moved by moving the fourth lens unit.

Further, a rear focus type is adopted in which the fourth lens unit is moved on the optical axis for focusing. The solid curve 4a and the dotted curve 4b of the fourth group shown in the same figure represent image plane fluctuations due to zooming from the wide-angle end to the telephoto end when focusing on an object at infinity and an object at a short distance, respectively. The movement locus for correction is shown. The first and third groups are fixed during zooming and focusing.

In this embodiment, the fourth lens group is moved to correct the image plane variation due to zooming, and the fourth lens group is moved to perform the focusing. Curve 4 in the figure
As shown in a and 4b, when the magnification is changed from the wide-angle end to the telephoto end, the object side is moved so as to have a convex locus.
As a result, the space between the third group and the fourth group is effectively used, and the total lens length is effectively shortened.

In the present embodiment, for example, when focusing from an object at infinity to a near object at the telephoto end, the fourth lens unit is moved forward as indicated by a straight line 4c in the figure.

In this embodiment, as compared with the case where the first group is extended and the focusing is performed in the conventional four-group zoom lens, the rear focus system as described above is adopted, and the effective lens diameter of the first group is increased. To prevent it.

In this embodiment, the third lens unit is composed of a single positive 31st lens, at least one lens surface of which has an aspherical surface, and the fourth lens unit includes the positive 41st lens and the negative 42nd lens. Consists of two lenses, and by providing an aspherical surface on at least one of the lens surfaces, the number of lenses is reduced while maintaining good optical performance, and the total lens length is shortened by shortening the distance between lens groups. Is doing effectively. Here, the positive lens and the negative lens forming the fourth group may be separated or cemented.

By arranging the aperture stop immediately before the third lens unit, aberration fluctuations due to the movable lens unit are reduced, and by shortening the distance between the lens units in front of the aperture stop, the front lens diameter is reduced. Achieved easily.

By specifying the refracting power and the like of each lens group as described above, the overall size of the lens system can be reduced, a predetermined back focus can be ensured, and the object distance can be improved over the entire zoom range. We have obtained a high zoom ratio zoom lens with optical performance.

Next, the technical meanings of the above conditional expressions will be described.

Conditional expression (1) relates to the ratio between the back focus and the focal length at the wide-angle end, and is mainly for obtaining a predetermined back focus while downsizing the entire lens system. If the lower limit of conditional expression (1) is exceeded and the back focus becomes too short, dust and the like adhering to the final lens surface will appear on the surface of the image pickup device and the image quality will be degraded.

Conditional expression (2) relates to the ratio of the combined focal length of the third group and the fourth group to the product of the zoom ratio and the back focus, and is effective for a certain amount of back focus while mainly reducing aberration fluctuations. It is for getting to. Conditional expression (2)
If the combined positive refractive power of the third group and the fourth group becomes too weak below the lower limit of, the back focus becomes short accordingly, and as described above, dust and the like adhering to the final lens surface together with the image. It is not good because it appears and adversely affects the image quality. Also, if the combined refractive power of the third and fourth groups becomes too strong, exceeding the upper limit of conditional expression (2), especially if the refractive power of the fourth group becomes too strong, aberrations during zooming and focusing will occur. It is not good because the fluctuations will increase.

The rear focus type zoom lens, which is the object of the present invention, can be achieved by satisfying the above-mentioned conditions. Further, the size of the lens system as a whole can be reduced and the entire zoom range and the entire object distance can be achieved. In order to obtain good optical performance, the following conditions should be satisfied.

(A) When the focal length of the second lens unit is f2, the imaging magnification of the second lens unit at the telephoto end is β2T, and the focal length of the entire system at the telephoto end is FT.

[0031]

[Equation 6] Satisfy the following conditions.

Conditional expression (3) is for effectively reducing the total length of the lens while suppressing the variation of aberration during zooming. If the negative refractive power of the second lens unit becomes too weak beyond the upper limit, the moving amount of the second lens unit must be increased in order to secure a constant zoom ratio, and the total lens length increases accordingly. Is coming. If the negative refracting power of the second lens group becomes too strong below the lower limit, the negative Petzval sum increases, the field curvature becomes large, and it becomes difficult to satisfactorily correct coma aberration. Absent. In addition, the variation in aberration accompanying zooming becomes large, which is not good.

If the absolute value of the imaging magnification at the telephoto end of the second lens unit becomes too small below the lower limit of conditional expression (4),
The amount of movement of the second lens unit for obtaining a predetermined zoom ratio increases, and the total lens length increases accordingly. Further, if the image forming magnification exceeds the upper limit and becomes too large, the sensitivity on the telephoto side becomes large, and the amount of movement accompanying the zooming of the fourth lens unit becomes large, so that the back focus becomes shorter, which is preferable. Absent.

(B) When the principal point spacing at the wide-angle end of the third group and the fourth group is e3w

[0035]

[Equation 7] Satisfy the following conditions.

When the distance between the principal points becomes too short beyond the lower limit of conditional expression (5), the moving space of the fourth lens unit when focusing is made small. Also, if the principal point interval becomes too long beyond the upper limit, it becomes difficult to secure a predetermined amount of back focus.

(C) When the radius of curvature of the image side lens surface of the 31st lens of the third group is R3, b

[0038]

[Equation 8] Satisfy the following conditions.

When the lower limit of conditional expression (6) is exceeded and the curvature of the image side lens surface of the thirty-first lens becomes gentle, the reflected light from the image pickup surface is reflected again by the lens surface and enters the image pickup surface. ,
It's not good because it becomes flare and ghost. If the upper limit is exceeded and the refractive power of the lens surface becomes too strong, it becomes difficult to correct the image plane variation due to zooming, which is not preferable.

When the lens surface is aspherical, the radius of curvature R3, b is a paraxial radius of curvature.

Next, numerical examples of the present invention will be shown. In the numerical examples, ri is the radius of curvature of the i-th lens surface in order from the object side, di is the i-th lens thickness and air gap from the object side, and ni and νi are the values of the i-th lens in order from the object side, respectively. The refractive index of glass and the Abbe number.

R18, r19 in Numerical Embodiments 1, 2, 4, 5, 6, 7 and r19, r2 in Numerical Embodiment 3.
Reference numeral 0 is a glass block such as a face plate.

The aspherical shape has an X axis in the optical axis direction, an H axis in the direction perpendicular to the optical axis, a positive light traveling direction, and R as a paraxial radius of curvature,
When A, B, C, and D are aspherical coefficients, respectively

[0044]

[Equation 9] It is expressed by the formula. <Numerical Example 1> f = 1 to 7.6 fno = 1: 1.85 to 2.65 2ω = 54 ° to 7.7 ° r 1 = 6.459 d 1 = 0.1562 n 1 = 1.80518 ν 1 = 25.4 r 2 = 2.944 d 2 = 0.5833 n 2 = 1.60311 ν 2 = 60.7 r 3 = 102.805 d 3 = 0.0417 r 4 = 2.902 d 4 = 0.4167 n 3 = 1.77250 ν 3 = 49.6 r 5 = 8.598 d 5 = variable r 6 = 3.909 d 6 = 0.1250 n 4 = 1.88300 ν 4 = 40.8 r 7 = 0.785 d 7 = 0.4631 r 8 = -1.308 d 8 = 0.1250 n 5 = 1.51742 ν 5 = 52.4 r 9 = 1.293 d 9 = 0.2917 n 6 = 1.84666 ν 6 = 23.9 r10 = -330.564 d10 = Variable r11 = Aperture d11 = 0.2188 r12 = 4.197 d12 = 0.5000 n 7 = 1.58313 ν 7 = 59.4 r13 = -4.143 d13 = Variable r14 = 2.905 d14 = 0.1458 n 8 = 1.84666 ν 8 = 23.9 r15 = 1.260 d15 = 0.0099 r16 = 1.303 d16 = 0.8750 n 9 = 1.58313 ν 9 = 59.4 r17 = -2.464 d17 = 0.8333 r18 = ∞ d18 = 0.8333 n10 = 1.51633 ν10 = 64.2 r19 = ∞

[0045]

[Table 1]

[0046]

[Table 2] <Numerical Example 2> f = 1 to 9.5 fno = 1: 1.85 to 2.65 2ω = 54 ° to 6.2 ° r 1 = 8.874 d 1 = 0.1562 n 1 = 1.80518 ν 1 = 25.4 r 2 = 3.819 d 2 = 0.6250 n 2 = 1.60311 ν 2 = 60.7 r 3 = -106.663 d 3 = 0.0521 r 4 = 3.567 d 4 = 0.4479 n 3 = 1.77250 ν 3 = 49.6 r 5 = 9.694 d 5 = variable r 6 = 3.249 d 6 = 0.1250 n 4 = 1.88300 ν 4 = 40.8 r 7 = 0.918 d 7 = 0.5763 r 8 = -1.304 d 8 = 0.1250 n 5 = 1.51742 ν 5 = 52.4 r 9 = 1.624 d 9 = 0.2917 n 6 = 1.84666 ν 6 = 23.9 r10 =- 41.068 d10 = Variable r11 = Aperture d11 = 0.2188 r12 = 3.348 d12 = 0.5312 n 7 = 1.58313 ν 7 = 59.4 r13 = -5.727 d13 = Variable r14 = 3.485 d14 = 0.1458 n 8 = 1.84666 ν 8 = 23.9 r15 = 1.440 d15 = 0.0139 r16 = 1.496 d16 = 0.7812 n 9 = 1.58313 ν 9 = 59.4 r17 = -2.804 d17 = 0.8333 r18 = ∞ d18 = 0.8333 n10 = 1.51633 ν10 = 64.2 r19 = ∞

[0047]

[Table 3]

[0048]

[Table 4] <Numerical Example 3> f = 1 to 7.6 fno = 1: 1.85 to 2.65 2ω = 54 ° to 7.7 ° r 1 = 6.585 d 1 = 0.1562 n 1 = 1.80518 ν 1 = 25.4 r 2 = 2.975 d 2 = 0.5833 n 2 = 1.60311 ν 2 = 60.7 r 3 = -311.492 d 3 = 0.0417 r 4 = 2.815 d 4 = 0.4167 n 3 = 1.77250 ν 3 = 49.6 r 5 = 7.929 d 5 = variable r 6 = 2.843 d 6 = 0.1250 n 4 = 1.88300 ν 4 = 40.8 r 7 = 0.912 d 7 = 0.4739 r 8 = -1.275 d 8 = 0.1250 n 5 = 1.56873 ν 5 = 63.2 r 9 = 1.325 d 9 = 0.0949 r10 = 1.683 d10 = 0.2917 n 6 = 1.84666 ν 6 = 23.9 r11 = 22.414 d11 = Variable r12 = Aperture d12 = 0.2188 r13 = 3.761 d13 = 0.5000 n 7 = 1.58313 ν 7 = 59.4 r14 = -4.456 d14 = Variable r15 = 2.886 d15 = 0.1458 n 8 = 1.84666 ν 8 = 23.9 r16 = 1.292 d16 = 0.0098 r17 = 1.340 d17 = 0.8750 n 9 = 1.58313 ν 9 = 59.4 r18 = -2.537 d18 = 0.8333 r19 = ∞ d19 = 0.8333 n10 = 1.51633 ν10 = 64.2 r20 = ∞

[0049]

[Table 5]

[0050]

[Table 6] <Numerical Example 4> f = 1 to 7.6 fno = 1: 1.85 to 2.65 2ω = 54 ° to 7.7 ° r 1 = 6.471 d 1 = 0.1562 n 1 = 1.80518 ν 1 = 25.4 r 2 = 2.939 d 2 = 0.5521 n 2 = 1.60311 ν 2 = 60.7 r 3 = 87.958 d 3 = 0.0417 r 4 = 3.069 d 4 = 0.3958 n 3 = 1.77250 ν 3 = 49.6 r 5 = 10.666 d 5 = variable r 6 = 5.513 d 6 = 0.1250 n 4 = 1.88300 ν 4 = 40.8 r 7 = 0.838 d 7 = 0.4343 r 8 = -1.368 d 8 = 0.1250 n 5 = 1.51742 ν 5 = 52.4 r 9 = 1.329 d 9 = 0.2708 n 6 = 1.84666 ν 6 = 23.9 r10 = -131.124 d10 = Variable r11 = Aperture d11 = 0.2188 r12 = 2.605 d12 = 0.5000 n 7 = 1.58313 ν 7 = 59.4 r13 = -14.156 d13 = Variable r14 = 2.831 d14 = 0.1458 n 8 = 1.84666 ν 8 = 23.9 r15 = 1.258 d15 = 0.0131 r16 = 1.311 d16 = 0.8750 n 9 = 1.58313 ν 9 = 59.4 r17 = -2.359 d17 = 0.8333 r18 = ∞ d18 = 0.8333 n10 = 1.51633 ν10 = 64.2 r19 = ∞

[0051]

[Table 7]

[0052]

[Table 8] <Numerical Example 5> f = 1 to 7.6 fno = 1: 1.85 to 2.65 2ω = 54 ° to 7.7 ° r 1 = 5.765 d 1 = 0.1562 n 1 = 1.80518 ν 1 = 25.4 r 2 = 2.765 d 2 = 0.5625 n 2 = 1.60311 ν 2 = 60.7 r 3 = 30.627 d 3 = 0.0417 r 4 = 2.864 d 4 = 0.4167 n 3 = 1.77250 ν 3 = 49.6 r 5 = 8.578 d 5 = variable r 6 = 4.004 d 6 = 0.1250 n 4 = 1.88300 ν 4 = 40.8 r 7 = 0.767 d 7 = 0.4543 r 8 = -1.421 d 8 = 0.1250 n 5 = 1.51742 ν 5 = 52.4 r 9 = 1.221 d 9 = 0.2917 n 6 = 1.84666 ν 6 = 23.9 r10 = 44.580 d10 = Variable r11 = Aperture d11 = 0.2188 r12 = 4.879 d12 = 0.4792 n 7 = 1.58313 ν 7 = 59.4 r13 = -3.472 d13 = Variable r14 = 2.982 d14 = 0.1458 n 8 = 1.84666 ν 8 = 23.9 r15 = 1.256 d15 = 0.0103 r16 = 1.304 d16 = 0.8750 n 9 = 1.58313 ν 9 = 59.4 r17 = -2.467 d17 = 0.8333 r18 = ∞ d18 = 0.8333 n10 = 1.51633 ν10 = 64.2 r19 = ∞

[0053]

[Table 9]

[0054]

[Table 10] <Numerical Example 6> f = 1 to 7.6 fno = 1: 1.85 to 2.65 2ω = 54 ° to 7.7 ° r 1 = 7.535 d 1 = 0.1562 n 1 = 1.80518 ν 1 = 25.4 r 2 = 3.144 d 2 = 0.5833 n 2 = 1.60311 ν 2 = 60.7 r 3 = -60.504 d 3 = 0.0417 r 4 = 2.951 d 4 = 0.4167 n 3 = 1.77250 ν 3 = 49.6 r 5 = 8.713 d 5 = variable r 6 = 4.607 d 6 = 0.1250 n 4 = 1.88300 ν 4 = 40.8 r 7 = 0.814 d 7 = 0.4535 r 8 = -1.338 d 8 = 0.1250 n 5 = 1.51742 ν 5 = 52.4 r 9 = 1.307 d 9 = 0.2917 n 6 = 1.84666 ν 6 = 23.9 r10 =- 383.302 d10 = Variable r11 = Aperture d11 = 0.2188 r12 = 4.584 d12 = 0.5000 n 7 = 1.58313 ν 7 = 59.4 r13 = -4.266 d13 = Variable r14 = 2.647 d14 = 0.1458 n 8 = 1.84666 ν 8 = 23.9 r15 = 1.240 d15 = 0.0027 r16 = 1.261 d16 = 0.8750 n 9 = 1.58313 ν 9 = 59.4 r17 = -2.679 d17 = 0.8333 r18 = ∞ d18 = 0.8333 n10 = 1.51633 ν10 = 64.2 r19 = ∞

[0055]

[Table 11]

[0056]

[Table 12] Aspheric coefficient <Numerical Example 7> f = 1 to 7.6 fno = 1: 1.85 to 2.65 2ω = 54 ° to 7.7 ° r 1 = 5.113 d 1 = 0.1562 n 1 = 1.78472 ν 1 = 25.7 r 2 = 3.075 d 2 = 0.2139 r 3 = 2.318 d 3 = 1.0905 n 2 = 1.60300 ν 2 = 65.5 r 4 = -8.430 d 4 = Variable r 5 = -23.904 d 5 = 0.1250 n 3 = 1.88300 ν 3 = 40.8 r 6 = 0.768 d 6 = 0.3658 r 7 = -1.376 d 7 = 0.1250 n 4 = 1.64328 ν 4 = 47.8 r 8 = 1.119 d 8 = 0.2917 n 5 = 1.85026 ν 5 = 32.3 r 9 = -2.955 d 9 = Variable r10 = Aperture d10 = 0.2188 r11 = 4.188 d11 = 0.5000 n 6 = 1.58313 ν 6 = 59.4 r12 = -4.392 d12 = Variable r13 = 2.446 d13 = 0.1458 n 7 = 1.84666 ν 7 = 23.9 r14 = 1.260 d14 = 0.0149 r15 = 1.350 d15 = 0.8750 n 8 = 1.58313 ν 8 = 59.4 r16 = -3.104 d16 = 0.8333 r17 = ∞ d17 = 0.8333 n 9 = 1.51633 ν 9 = 64.2 r18 = ∞

[0057]

[Table 13]

[0058]

[Table 14]

[0059]

[Table 15]

[0060]

According to the present invention, as described above, the refracting powers of the four lens groups, the moving conditions of the second and fourth groups during zooming, and the combined refracting powers of the third and fourth groups are set. In addition, by adopting a lens structure that moves the fourth lens unit during focusing, a predetermined back focus is secured while the overall size of the lens system is reduced, and a zoom ratio of about 8 to 10 is achieved over the entire zoom range. It is possible to achieve a rear focus type zoom lens having an F number of about 1.8 and a large aperture ratio, which has high optical performance with little aberration variation during focusing while achieving good aberration correction.

[Brief description of drawings]

FIG. 1 is an explanatory view of a paraxial refractive power arrangement of the present invention.

FIG. 2 is a lens cross-sectional view of Numerical Example 1 of the present invention.

FIG. 3 is a lens sectional view of Numerical Example 2 of the present invention.

FIG. 4 is a lens cross-sectional view of Numerical Example 3 of the present invention.

FIG. 5 is a lens cross-sectional view of Numerical Example 4 of the present invention.

FIG. 6 is a lens cross-sectional view of Numerical Example 5 of the present invention.

FIG. 7 is a lens cross-sectional view of Numerical Example 6 of the present invention.

FIG. 8 is a lens cross-sectional view of Numerical Example 7 of the present invention.

FIG. 9 is a diagram of various types of aberration at the wide-angle end according to Numerical Example 1 of the present invention.

FIG. 10 is a diagram of various types of aberration at the telephoto end according to Numerical Example 1 of the present invention.

FIG. 11 is a diagram of various types of aberration at the wide-angle end according to Numerical Example 2 of the present invention.

FIG. 12 is a diagram of various types of aberration at the telephoto end according to Numerical Example 2 of the present invention.

FIG. 13 is a diagram of various types of aberration at the wide-angle end according to Numerical Example 3 of the present invention.

FIG. 14 is a diagram of various types of aberration at the telephoto end according to Numerical Example 3 of the present invention.

FIG. 15 is a diagram of various types of aberration at the wide-angle end according to Numerical Example 4 of the present invention.

FIG. 16 is a diagram showing various types of aberration at the telephoto end according to Numerical Example 4 of the present invention.

FIG. 17 is a diagram of various types of aberration at the wide-angle end according to Numerical Example 5 of the present invention.

FIG. 18 is a diagram of various types of aberration at the telephoto end according to Numerical Example 5 of the present invention.

FIG. 19 is a diagram of various types of aberration at the wide-angle end according to Numerical Example 6 of the present invention.

FIG. 20 is a diagram of various types of aberration at the telephoto end according to Numerical Example 6 of the present invention.

FIG. 21 is a diagram of various types of aberration at the wide-angle end according to Numerical Example 7 of the present invention.

FIG. 22 is a diagram of various types of aberration at the telephoto end according to Numerical Example 7 of the present invention.

[Explanation of symbols]

 L1 1st group L2 2nd group L3 3rd group L4 4th group SP Aperture ΔS Sagittal image surface ΔM Meridional image surface

Claims (4)

[Claims] 1. Four lens groups, a first group having a positive refractive power, a second group having a negative refractive power, a third group having a positive refractive power, and a fourth group having a positive refractive power, in order from the object side. And moving the second lens unit toward the image side to perform zooming from the wide-angle end to the telephoto end, and moving the fourth lens unit to correct the image surface variation due to zooming and The third group is made up of a positive thirty-first lens having an aspherical surface, and the fourth group is made up of a negative forty-first lens and a positive forty-second lens.
At least one lens surface of the lens and the 42nd lens is formed of an aspherical surface, the combined focal lengths of the third group and the fourth group at the wide-angle end are f3, 4 and the focal length of the entire system at the wide-angle end is Fw, When the distance from the lens final surface to the image surface, which is the shortest in the entire zoom range, is Fb and the zoom ratio is Z while focusing on an object at infinity. A rear focus type zoom lens characterized by satisfying the following conditions. 2. When the focal length of the second lens unit is f2, the imaging magnification of the second lens unit at the telephoto end is β2T, and the focal length of the entire system at the telephoto end is FT, ## EQU2 ## The rear focus type zoom lens according to claim 1, wherein the following condition is satisfied. 3. When the principal point interval between the third group and the fourth group at the wide-angle end is e3w: The rear focus type zoom lens according to claim 2, wherein the following condition is satisfied. 4. When the radius of curvature of the image side lens surface of the 31st lens of the third group is R3, b The rear focus type zoom lens according to claim 3, wherein the following condition is satisfied.